(1) Field of the Invention
This invention relates to a weighing system as part of a helicopter, particularly to a weighing system taking into account as well external loads of the helicopter with the features of the preamble of claim 1 and methods of operating such a weighing system with a function in the same system to take into account as well external loads of the helicopter with the features of the preamble of claim 11.
(2) Description of Related Art
Critical factors in the flight or at take off of any aircraft are the weight and balance of such an aircraft. An aircraft manufacturer must insure that sufficient lift is generated at take-off to lift the weight of the airplane. A second but equally important factor to consider is whether the aircraft is in balance, i. e. whether the location for the center of gravity of the aircraft is within allowable limits.
Calculations to determine weight and center of gravity of an aircraft are known and documented.
The document U.S. Pat. No. 4,780,838 (A) discloses a helicopter weight and torque advisory system for connection to cargo hook load sensors, fuel flow, air temperature and altitude indicating systems of a helicopter. The advisory system provides the flight crew of the helicopter information as to available engine torque, gross weight, gross weight center of gravity condition and weight supported by each cargo hook as an external sling load is raised and supported by the helicopter. Information as to operating weight empty, fuel weight and center of gravity are to be entered manually. External cargo hook load sensors are provided and displays showing the individual loads supported by each external load hook.
The document EP 0625260 (A1) discloses an onboard system for use in measuring, computing and displaying the gross weight and location/relocation of the center of gravity for an aircraft. Temperature and pressure transmitters and transducers are mounted in relation to each of the landing gear struts for transmission of said temperature and pressure signals to an onboard micro-computer/controller with redundancy for accuracy and failure protection. The system also incorporates a software correction program to correct and compensate for physical changes to strut components due to temperature fluctuations, O-ring seal drag and hysteresis within modern day “shock absorbing” aircraft landing gear struts. The computer makes adjustments for internal temperature changes and drag; converts sustained pressures to the weight supported by each strut, and computes the aircraft's current gross weight and center of gravity. The computer also is pre-programmed to illuminate a “Hard Landing Indicator Light” mounted on the display, when pre-programmed individual strut pressure limits are exceeded and sensed during landing. These pressure readings are stored in the computer memory and can be utilized when the aircraft is inspected and serviced. The use of temperature and pressure transmitters and transducers in relation to each of the landing gear struts renders this state of the art complex, expensive and inefficient for maintenance.
The document US 2010063718 (A1) describes a system for continuous monitoring of center of gravity and total weight of an airplane at rest on the ground. Information from strain gauge transducers located on structural members for the nose wheel and main landing gear is communicated to a computer where calculations are made and data is transmitted to gauges in the airplane cockpit. Range limits for the airplane center of gravity with respect to the center of lift, and also the total airplane weight overload limit are clearly indicated on the respective gauges. A marking on said gauges indicate overload. Said system for continuous monitoring is not suitable for a helicopter with a skid type landing gear. Extra loads outside an airplane are not a configuration to be considered for the design of said airplane of the state of the art.
The document U.S. Pat. No. 4,637,575 A discloses a work platform and helicopter assembly for working on a high-voltage power line such as an EHV power line. A work platform comprising a rectangular base of electrically conductive material is disposed transversely across a pair of helicopter skid tubes that extend longitudinally beneath the helicopter fuselage. The work platform is attached to the skid tubes such that the skid tubes may be laterally displaceable, upon landing, or take-off, with respect to the work platform. The work platform includes a workman supporting portion that extends laterally from the side of at least one skid tube to support a workman working on a high-voltage power line. The work platform, skid tubes and helicopter are electrically connected so that they will all be at the same electrical potential when working on a power line. The work platform may include a portion adapted to carry cargo between the skid tubes. A ballast is provided to the work platform, at the end of the work platform opposite from the workman supporting portion, so as to maintain the helicopter with the lateral center of gravity limits.
The document U.S. Pat. No. 5,109,580 A discloses a clamp assembly primarily designed for the removable attachment of a load supporting device to a skid or like support structure of a helicopter such that additional load or cargo may be mounted exteriorally of the helicopter body and generally between the supporting skid assembly and the cockpit or other interior cargo space. The clamp assembly is removably secured to the load supporting structure and includes two clamp body segments pivotal relative to one another between an open position and a clamped position, the latter being defined by a gripping or clamping of the clamp segment about the generally tubular structure defining the skid assembly.
The document WO 2006022700 A1 discloses a weight-on-gear sensor for use on an aircraft with landing skids having a bracket and a displacement sensor attached to the bracket. The bracket has a center member connecting a first end member to a second end member. The center member has a centerline and the end members extend from the centerline of the center member. Mounting members extend along the centerline of the center member to facilitate attachment of the bracket to a cross tube. The displacement sensor connects the first end member to the second end member. The displacement sensor is parallel to, and offset from, the centerline of the center member so that when a bending moment is applied to the center member the first displacement sensor is either elongated or shortened.
The document U.S. Pat. No. 4,850,552 A discloses a landing gear load sensor for an aircraft having a skid type landing gear. The sensor includes a shear beam having a load bearing area. Structure is provided for mounting the shear beam to the aircraft, such that the load bearing area is disposed adjacent the landing gear. Structure is disposed on the shear beam between the mounting structure and the load bearing area for sensing shear load on the shear beam.